Steve's Homepage


Honda 1998 CBR900RR

Line Art Courtesy American Honda

Here's a color rendition of the lightly modified 1998 CBR900RR frame -- a fringe plot used in finite element analysis, a CAD system for loading an item inside a computer to measure its strength.
Showroom success is much easier with a radical-looking machine. So Honda redesigned the RR's upper cowl to provide a more "organic" look. Protection at speed is excellent, with the "bubble" offering a nice, quiet place for the rider to relax while barreling down the road at illegal speeds.
"Some chassis flex is good," announced a Honda spokesperson at an RR press conference. Jaws dropped. "For street compliance, that is." Maybe so, but on the racetrack frame flex sucks, and it seems Honda was tired of getting hammered by journalists and racers. So lateral (side-to-side) and torsional (twisting) stiffness was significantly improved in the new frame by beefing up the lower section's wall thickness.
The '98 CBR900 sports Honda's first tapered box-section aluminum swingarm, similar to those found on last year's Yamaha YZF600.

The new swingarm is significantly stronger: Torsional rigidity is up 19.5 percent, while lateral stiffness increased a whopping 37.4 percent.

Taming the beast: 5mm more trail means the fork tubes are 5mm closer to the frame (trail is the distance, measured on the ground, between the center of the front wheel and a line drawn out from the steering head that meets the ground in front of the wheel. Thus, moving the front wheel back adds trail). This is good: Added trail has been a common modification made by racers to increase stability to previous years' CBR900RRs. The lower triple clamps are now made of aluminum instead of steel and increase fork span 10mm, resulting in a 10 percent increase in rigidity.
Gear ratios have been widened up, reducing the amount of shifting needed during street riding -- MO staffers tend to prefer wide-ratio five-speeds with decent midrange power, thus we liked the new ratios, especially since the motor has been made much smoother and more responsive. Racers, however, will want the closer ratios offered last year.